1. Field of the Invention
The present invention relates to a printing apparatus for establishing a priority identifier and a method of establishing a priority identifier, and more particularly, to a printing apparatus capable of establishing a priority identifier in various forms and methods to process an instruction, designated by the priority identifier, before another instruction.
2. Description of the Related Art
In general, printing apparatuses are connected to personal computers to print out documents or pictures. Also, printing apparatuses may be provided in data processing apparatuses such as point-of-sale (POS) terminals or electronic cash registers used for monetary transactions, to print out receipts and the like. Those printing apparatuses perform operations, including printing, in response to print data and instructions sent from host computers including personal computers.
For example, FIG. 1 is a block diagram illustrating the basic hardware configuration of a printing apparatus. The printing apparatus includes an interface unit 1 receiving data from a host computer or sending data to the host computer, a memory unit 2 storing various pieces of data, a print driving unit 4 controlling the driving of mechanical components within the printing apparatus, for example, a print part 6, a motor part 7 and flange parts 8, a sensor unit 5 detecting the status of the printing apparatus, and a central processing unit (CPU) 3 controlling the operation of the print driving unit 4 by checking data or instructions sent from the host computer via the interface unit 1 and checking the status of the printing apparatus based on the output signal of the sensor unit 5.
Printing apparatuses at an early stage of development interpreted and processed control instructions in First-In, First-out (FIFO) order. However, when an error occurs during the use of a printing apparatus, such as when paper supply is depleted or a printer cover is opened, or as an occasion arises, an instruction delivered later may need to be processed before an instruction delivered earlier. In response to this need, U.S. Pat. No. 5,594,653 discloses a printing apparatus that divides commands into instructions to be processed in real-time (hereinafter, referred to as ‘real-time instructions’) and instructions to be processed in FIFO order (hereinafter, referred to as ‘general instructions’) and enables the real-time instruction to be processed preferentially (i.e., first) over general instructions.
However, if a command itself is determined to be a real-time instruction or a general instruction, every necessary real-time command needs to be established in advance by anticipating every possible circumstance that may occur in the printing apparatus at the time of command implementation. In this regard, a printing apparatus has been proposed that establishes an identifier for designating priority processing (hereinafter, referred to as ‘priority identifier’) in advance, and enables an instruction designated by the priority identifier to be processed preferentially over other instructions. However, this method may also be disadvantageous, in that the previously established prior-processing identifier restricts command implementation.